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author | Sverker Eriksson <sverker@erlang.org> | 2015-11-26 19:56:51 +0100 |
---|---|---|
committer | Sverker Eriksson <sverker@erlang.org> | 2015-11-26 19:56:51 +0100 |
commit | 4e91911aec363d21ea2d6ff7d5f8e1888b0aa8f9 (patch) | |
tree | 5b151ec5340a85af698ae3bceb21a2a8ab390548 /erts | |
parent | a89f1cd881396fc6445b7d790ee2f5b7ae5a6031 (diff) | |
parent | 949de78331b9c4ecb9c628bb651cecb113790e2e (diff) | |
download | otp-4e91911aec363d21ea2d6ff7d5f8e1888b0aa8f9.tar.gz otp-4e91911aec363d21ea2d6ff7d5f8e1888b0aa8f9.tar.bz2 otp-4e91911aec363d21ea2d6ff7d5f8e1888b0aa8f9.zip |
Merge branch 'sverk/setnode-rename-bug/OTP-13076' into maint
* sverk/setnode-rename-bug/OTP-13076:
erts: Fix bug in setnode/2
erts: Remove ERTS_PSD_DIST_ENTRY
erts: Remove faulty ASSERT in erts_proc_*_refc
Diffstat (limited to 'erts')
-rw-r--r-- | erts/emulator/beam/bif.c | 1 | ||||
-rw-r--r-- | erts/emulator/beam/dist.c | 23 | ||||
-rw-r--r-- | erts/emulator/beam/erl_node_tables.c | 150 | ||||
-rw-r--r-- | erts/emulator/beam/erl_process.c | 11 | ||||
-rw-r--r-- | erts/emulator/beam/erl_process.h | 17 | ||||
-rw-r--r-- | erts/emulator/test/distribution_SUITE_data/run.erl | 47 |
6 files changed, 102 insertions, 147 deletions
diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c index 0bd46a2dae..a8cc19ee1f 100644 --- a/erts/emulator/beam/bif.c +++ b/erts/emulator/beam/bif.c @@ -4231,6 +4231,7 @@ BIF_RETTYPE list_to_pid_1(BIF_ALIST_1) goto bad; enp = erts_find_or_insert_node(dep->sysname, dep->creation); + ASSERT(enp != erts_this_node); etp = (ExternalThing *) HAlloc(BIF_P, EXTERNAL_THING_HEAD_SIZE + 1); etp->header = make_external_pid_header(1); diff --git a/erts/emulator/beam/dist.c b/erts/emulator/beam/dist.c index 0bbcc5f966..4846133aa6 100644 --- a/erts/emulator/beam/dist.c +++ b/erts/emulator/beam/dist.c @@ -2576,7 +2576,9 @@ int distribution_info(int to, void *arg) /* Called by break handler */ } for (dep = erts_not_connected_dist_entries; dep; dep = dep->next) { - info_dist_entry(to, arg, dep, 0, 0); + if (dep != erts_this_dist_entry) { + info_dist_entry(to, arg, dep, 0, 0); + } } return(0); @@ -2654,13 +2656,8 @@ BIF_RETTYPE setnode_2(BIF_ALIST_2) if (!net_kernel) goto error; - /* By setting dist_entry==erts_this_dist_entry and DISTRIBUTION on - net_kernel do_net_exist will be called when net_kernel - is terminated !! */ - (void) ERTS_PROC_SET_DIST_ENTRY(net_kernel, - ERTS_PROC_LOCK_MAIN, - erts_this_dist_entry); - erts_refc_inc(&erts_this_dist_entry->refc, 2); + /* By setting F_DISTRIBUTION on net_kernel, + * do_net_exist will be called when net_kernel is terminated !! */ net_kernel->flags |= F_DISTRIBUTION; if (net_kernel != BIF_P) @@ -3021,11 +3018,11 @@ BIF_RETTYPE nodes_1(BIF_ALIST_1) erts_smp_rwmtx_rlock(&erts_dist_table_rwmtx); - ASSERT(erts_no_of_not_connected_dist_entries >= 0); + ASSERT(erts_no_of_not_connected_dist_entries > 0); ASSERT(erts_no_of_hidden_dist_entries >= 0); ASSERT(erts_no_of_visible_dist_entries >= 0); if(not_connected) - length += erts_no_of_not_connected_dist_entries; + length += (erts_no_of_not_connected_dist_entries - 1); if(hidden) length += erts_no_of_hidden_dist_entries; if(visible) @@ -3047,8 +3044,10 @@ BIF_RETTYPE nodes_1(BIF_ALIST_1) #endif if(not_connected) for(dep = erts_not_connected_dist_entries; dep; dep = dep->next) { - result = CONS(hp, dep->sysname, result); - hp += 2; + if (dep != erts_this_dist_entry) { + result = CONS(hp, dep->sysname, result); + hp += 2; + } } if(hidden) for(dep = erts_hidden_dist_entries; dep; dep = dep->next) { diff --git a/erts/emulator/beam/erl_node_tables.c b/erts/emulator/beam/erl_node_tables.c index 2fb790b953..a7d0511bf9 100644 --- a/erts/emulator/beam/erl_node_tables.c +++ b/erts/emulator/beam/erl_node_tables.c @@ -37,18 +37,18 @@ erts_smp_rwmtx_t erts_node_table_rwmtx; DistEntry *erts_hidden_dist_entries; DistEntry *erts_visible_dist_entries; -DistEntry *erts_not_connected_dist_entries; +DistEntry *erts_not_connected_dist_entries; /* including erts_this_dist_entry */ Sint erts_no_of_hidden_dist_entries; Sint erts_no_of_visible_dist_entries; -Sint erts_no_of_not_connected_dist_entries; +Sint erts_no_of_not_connected_dist_entries; /* including erts_this_dist_entry */ DistEntry *erts_this_dist_entry; ErlNode *erts_this_node; char erts_this_node_sysname_BUFFER[256], *erts_this_node_sysname = "uninitialized yet"; -static Uint node_entries; -static Uint dist_entries; +static Uint node_entries = 0; +static Uint dist_entries = 0; static int references_atoms_need_init = 1; @@ -91,9 +91,6 @@ dist_table_alloc(void *dep_tmpl) erts_smp_rwmtx_opt_t rwmtx_opt = ERTS_SMP_RWMTX_OPT_DEFAULT_INITER; rwmtx_opt.type = ERTS_SMP_RWMTX_TYPE_FREQUENT_READ; - if(((DistEntry *) dep_tmpl) == erts_this_dist_entry) - return dep_tmpl; - sysname = ((DistEntry *) dep_tmpl)->sysname; chnl_nr = make_small((Uint) atom_val(sysname)); dep = (DistEntry *) erts_alloc(ERTS_ALC_T_DIST_ENTRY, sizeof(DistEntry)); @@ -132,7 +129,9 @@ dist_table_alloc(void *dep_tmpl) /* Link in */ - /* All new dist entries are "not connected" */ + /* All new dist entries are "not connected". + * erts_this_dist_entry is also always included among "not connected" + */ dep->next = erts_not_connected_dist_entries; if(erts_not_connected_dist_entries) { ASSERT(erts_not_connected_dist_entries->prev == NULL); @@ -149,9 +148,6 @@ dist_table_free(void *vdep) { DistEntry *dep = (DistEntry *) vdep; - if(dep == erts_this_dist_entry) - return; - ASSERT(is_nil(dep->cid)); ASSERT(dep->nlinks == NULL); ASSERT(dep->node_links == NULL); @@ -186,7 +182,7 @@ dist_table_free(void *vdep) #endif erts_free(ERTS_ALC_T_DIST_ENTRY, (void *) dep); - ASSERT(dist_entries > 1); + ASSERT(dist_entries > 0); dist_entries--; } @@ -306,7 +302,7 @@ static void try_delete_dist_entry(void *vdep) * thread incremented refc twice. Once for the new reference * and once for this thread. * - * If refc reach -1, noone has used the entry since we + * If refc reach -1, no one has used the entry since we * set up the timer. Delete the entry. * * If refc reach 0, the entry is currently not in use @@ -369,8 +365,7 @@ erts_dist_table_size(void) ASSERT(dist_entries == (erts_no_of_visible_dist_entries + erts_no_of_hidden_dist_entries - + erts_no_of_not_connected_dist_entries - + 1 /* erts_this_dist_entry */)); + + erts_no_of_not_connected_dist_entries)); #endif res = (hash_table_sz(&erts_dist_table) @@ -543,9 +538,6 @@ node_table_alloc(void *venp_tmpl) { ErlNode *enp; - if(((ErlNode *) venp_tmpl) == erts_this_node) - return venp_tmpl; - enp = (ErlNode *) erts_alloc(ERTS_ALC_T_NODE_ENTRY, sizeof(ErlNode)); node_entries++; @@ -563,8 +555,7 @@ node_table_free(void *venp) { ErlNode *enp = (ErlNode *) venp; - if(enp == erts_this_node) - return; + ERTS_SMP_LC_ASSERT(enp != erts_this_node || erts_thr_progress_is_blocking()); erts_deref_dist_entry(enp->dist_entry); #ifdef DEBUG @@ -572,7 +563,7 @@ node_table_free(void *venp) #endif erts_free(ERTS_ALC_T_NODE_ENTRY, venp); - ASSERT(node_entries > 1); + ASSERT(node_entries > 0); node_entries--; } @@ -650,7 +641,7 @@ static void try_delete_node(void *venp) * thread incremented refc twice. Once for the new reference * and once for this thread. * - * If refc reach -1, noone has used the entry since we + * If refc reach -1, no one has used the entry since we * set up the timer. Delete the entry. * * If refc reach 0, the entry is currently not in use @@ -747,25 +738,20 @@ void erts_print_node_info(int to, void erts_set_this_node(Eterm sysname, Uint creation) { - erts_smp_rwmtx_rwlock(&erts_node_table_rwmtx); - erts_smp_rwmtx_rwlock(&erts_dist_table_rwmtx); + ERTS_SMP_LC_ASSERT(erts_thr_progress_is_blocking()); + ASSERT(erts_refc_read(&erts_this_dist_entry->refc, 2)); - (void) hash_erase(&erts_dist_table, (void *) erts_this_dist_entry); - erts_this_dist_entry->sysname = sysname; - erts_this_dist_entry->creation = creation; - (void) hash_put(&erts_dist_table, (void *) erts_this_dist_entry); + if (erts_refc_dectest(&erts_this_node->refc, 0) == 0) + try_delete_node(erts_this_node); - (void) hash_erase(&erts_node_table, (void *) erts_this_node); - erts_this_node->sysname = sysname; - erts_this_node->creation = creation; - erts_this_node_sysname = erts_this_node_sysname_BUFFER; - erts_snprintf(erts_this_node_sysname, sizeof(erts_this_node_sysname_BUFFER), - "%T", sysname); - (void) hash_put(&erts_node_table, (void *) erts_this_node); + if (erts_refc_dectest(&erts_this_dist_entry->refc, 0) == 0) + try_delete_dist_entry(erts_this_dist_entry); - erts_smp_rwmtx_rwunlock(&erts_dist_table_rwmtx); - erts_smp_rwmtx_rwunlock(&erts_node_table_rwmtx); + erts_this_node = NULL; /* to make sure refc is bumped for this node */ + erts_this_node = erts_find_or_insert_node(sysname, creation); + erts_this_dist_entry = erts_this_node->dist_entry; + erts_refc_inc(&erts_this_dist_entry->refc, 2); } Uint @@ -782,6 +768,7 @@ void erts_init_node_tables(int dd_sec) { erts_smp_rwmtx_opt_t rwmtx_opt = ERTS_SMP_RWMTX_OPT_DEFAULT_INITER; HashFunctions f; + ErlNode node_tmpl; if (dd_sec == ERTS_NODE_TAB_DELAY_GC_INFINITY) node_tab_delete_delay = (ErtsMonotonicTime) -1; @@ -793,16 +780,21 @@ void erts_init_node_tables(int dd_sec) rwmtx_opt.type = ERTS_SMP_RWMTX_TYPE_FREQUENT_READ; rwmtx_opt.lived = ERTS_SMP_RWMTX_LONG_LIVED; + erts_smp_rwmtx_init_opt(&erts_node_table_rwmtx, &rwmtx_opt, "node_table"); + erts_smp_rwmtx_init_opt(&erts_dist_table_rwmtx, &rwmtx_opt, "dist_table"); + f.hash = (H_FUN) dist_table_hash; f.cmp = (HCMP_FUN) dist_table_cmp; f.alloc = (HALLOC_FUN) dist_table_alloc; f.free = (HFREE_FUN) dist_table_free; - - erts_this_dist_entry = erts_alloc(ERTS_ALC_T_DIST_ENTRY, sizeof(DistEntry)); - dist_entries = 1; - hash_init(ERTS_ALC_T_DIST_TABLE, &erts_dist_table, "dist_table", 11, f); + f.hash = (H_FUN) node_table_hash; + f.cmp = (HCMP_FUN) node_table_cmp; + f.alloc = (HALLOC_FUN) node_table_alloc; + f.free = (HFREE_FUN) node_table_free; + hash_init(ERTS_ALC_T_NODE_TABLE, &erts_node_table, "node_table", 11, f); + erts_hidden_dist_entries = NULL; erts_visible_dist_entries = NULL; erts_not_connected_dist_entries = NULL; @@ -810,69 +802,23 @@ void erts_init_node_tables(int dd_sec) erts_no_of_visible_dist_entries = 0; erts_no_of_not_connected_dist_entries = 0; - erts_this_dist_entry->next = NULL; - erts_this_dist_entry->prev = NULL; - erts_refc_init(&erts_this_dist_entry->refc, 1); /* erts_this_node */ - - erts_smp_rwmtx_init_opt_x(&erts_this_dist_entry->rwmtx, - &rwmtx_opt, - "dist_entry", - make_small(ERST_INTERNAL_CHANNEL_NO)); - erts_this_dist_entry->sysname = am_Noname; - erts_this_dist_entry->cid = NIL; - erts_this_dist_entry->connection_id = 0; - erts_this_dist_entry->status = 0; - erts_this_dist_entry->flags = 0; - erts_this_dist_entry->version = 0; - - erts_smp_mtx_init_x(&erts_this_dist_entry->lnk_mtx, - "dist_entry_links", - make_small(ERST_INTERNAL_CHANNEL_NO)); - erts_this_dist_entry->node_links = NULL; - erts_this_dist_entry->nlinks = NULL; - erts_this_dist_entry->monitors = NULL; - - erts_smp_mtx_init_x(&erts_this_dist_entry->qlock, - "dist_entry_out_queue", - make_small(ERST_INTERNAL_CHANNEL_NO)); - erts_this_dist_entry->qflgs = 0; - erts_this_dist_entry->qsize = 0; - erts_this_dist_entry->out_queue.first = NULL; - erts_this_dist_entry->out_queue.last = NULL; - erts_this_dist_entry->suspended = NULL; - - erts_this_dist_entry->finalized_out_queue.first = NULL; - erts_this_dist_entry->finalized_out_queue.last = NULL; - erts_smp_atomic_init_nob(&erts_this_dist_entry->dist_cmd_scheduled, 0); - erts_port_task_handle_init(&erts_this_dist_entry->dist_cmd); - erts_this_dist_entry->send = NULL; - erts_this_dist_entry->cache = NULL; - - (void) hash_put(&erts_dist_table, (void *) erts_this_dist_entry); - - f.hash = (H_FUN) node_table_hash; - f.cmp = (HCMP_FUN) node_table_cmp; - f.alloc = (HALLOC_FUN) node_table_alloc; - f.free = (HFREE_FUN) node_table_free; + node_tmpl.sysname = am_Noname; + node_tmpl.creation = 0; + erts_this_node = hash_put(&erts_node_table, &node_tmpl); + /* +1 for erts_this_node */ + erts_refc_init(&erts_this_node->refc, 1); - hash_init(ERTS_ALC_T_NODE_TABLE, &erts_node_table, "node_table", 11, f); + ASSERT(erts_this_node->dist_entry != NULL); + erts_this_dist_entry = erts_this_node->dist_entry; + /* +1 for erts_this_dist_entry */ + /* +1 for erts_this_node->dist_entry */ + erts_refc_init(&erts_this_dist_entry->refc, 2); - erts_this_node = erts_alloc(ERTS_ALC_T_NODE_ENTRY, sizeof(ErlNode)); - node_entries = 1; - erts_refc_init(&erts_this_node->refc, 1); /* The system itself */ - erts_this_node->sysname = am_Noname; - erts_this_node->creation = 0; - erts_this_node->dist_entry = erts_this_dist_entry; erts_this_node_sysname = erts_this_node_sysname_BUFFER; erts_snprintf(erts_this_node_sysname, sizeof(erts_this_node_sysname_BUFFER), "%T", erts_this_node->sysname); - (void) hash_put(&erts_node_table, (void *) erts_this_node); - - erts_smp_rwmtx_init_opt(&erts_node_table_rwmtx, &rwmtx_opt, "node_table"); - erts_smp_rwmtx_init_opt(&erts_dist_table_rwmtx, &rwmtx_opt, "dist_table"); - references_atoms_need_init = 1; } @@ -1410,6 +1356,10 @@ setup_reference_table(void) SYSTEM_REF, TUPLE2(&heap[0], AM_system, am_undefined)); + insert_dist_entry(erts_this_dist_entry, + SYSTEM_REF, + TUPLE2(&heap[0], AM_system, am_undefined), + erts_this_node->creation); UnUseTmpHeapNoproc(3); max = erts_ptab_max(&erts_proc); @@ -1472,12 +1422,6 @@ setup_reference_table(void) insert_links(ERTS_P_LINKS(proc), proc->common.id); if (ERTS_P_MONITORS(proc)) insert_monitors(ERTS_P_MONITORS(proc), proc->common.id); - /* Insert controller */ - { - DistEntry *dep = ERTS_PROC_GET_DIST_ENTRY(proc); - if (dep) - insert_dist_entry(dep, CTRL_REF, proc->common.id, 0); - } } } diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c index 3b1b593d1c..d583118e7b 100644 --- a/erts/emulator/beam/erl_process.c +++ b/erts/emulator/beam/erl_process.c @@ -625,11 +625,6 @@ erts_pre_init_process(void) erts_psd_required_locks[ERTS_PSD_SCHED_ID].set_locks = ERTS_PSD_SCHED_ID_SET_LOCKS; - erts_psd_required_locks[ERTS_PSD_DIST_ENTRY].get_locks - = ERTS_PSD_DIST_ENTRY_GET_LOCKS; - erts_psd_required_locks[ERTS_PSD_DIST_ENTRY].set_locks - = ERTS_PSD_DIST_ENTRY_SET_LOCKS; - erts_psd_required_locks[ERTS_PSD_CALL_TIME_BP].get_locks = ERTS_PSD_CALL_TIME_BP_GET_LOCKS; erts_psd_required_locks[ERTS_PSD_CALL_TIME_BP].set_locks @@ -12373,9 +12368,7 @@ erts_continue_exit_process(Process *p) erts_proc_dec_refc(p); } - dep = ((p->flags & F_DISTRIBUTION) - ? ERTS_PROC_SET_DIST_ENTRY(p, ERTS_PROC_LOCKS_ALL, NULL) - : NULL); + dep = (p->flags & F_DISTRIBUTION) ? erts_this_dist_entry : NULL; scb = ERTS_PROC_SET_SAVED_CALLS_BUF(p, ERTS_PROC_LOCKS_ALL, NULL); pbt = ERTS_PROC_SET_CALL_TIME(p, ERTS_PROC_LOCKS_ALL, NULL); nif_export = ERTS_PROC_SET_NIF_TRAP_EXPORT(p, ERTS_PROC_LOCKS_ALL, NULL); @@ -12387,8 +12380,6 @@ erts_continue_exit_process(Process *p) if (dep) { erts_do_net_exits(dep, reason); - if(dep) - erts_deref_dist_entry(dep); } /* diff --git a/erts/emulator/beam/erl_process.h b/erts/emulator/beam/erl_process.h index 20ffe7ea7c..10c6fa4a67 100644 --- a/erts/emulator/beam/erl_process.h +++ b/erts/emulator/beam/erl_process.h @@ -801,12 +801,11 @@ erts_smp_reset_max_len(ErtsRunQueue *rq, ErtsRunQueueInfo *rqi) #define ERTS_PSD_ERROR_HANDLER 0 #define ERTS_PSD_SAVED_CALLS_BUF 1 #define ERTS_PSD_SCHED_ID 2 -#define ERTS_PSD_DIST_ENTRY 3 -#define ERTS_PSD_CALL_TIME_BP 4 -#define ERTS_PSD_DELAYED_GC_TASK_QS 5 -#define ERTS_PSD_NIF_TRAP_EXPORT 6 +#define ERTS_PSD_CALL_TIME_BP 3 +#define ERTS_PSD_DELAYED_GC_TASK_QS 4 +#define ERTS_PSD_NIF_TRAP_EXPORT 5 -#define ERTS_PSD_SIZE 7 +#define ERTS_PSD_SIZE 6 typedef struct { void *data[ERTS_PSD_SIZE]; @@ -824,9 +823,6 @@ typedef struct { #define ERTS_PSD_SCHED_ID_GET_LOCKS ERTS_PROC_LOCK_STATUS #define ERTS_PSD_SCHED_ID_SET_LOCKS ERTS_PROC_LOCK_STATUS -#define ERTS_PSD_DIST_ENTRY_GET_LOCKS ERTS_PROC_LOCK_MAIN -#define ERTS_PSD_DIST_ENTRY_SET_LOCKS ERTS_PROC_LOCK_MAIN - #define ERTS_PSD_CALL_TIME_BP_GET_LOCKS ERTS_PROC_LOCK_MAIN #define ERTS_PSD_CALL_TIME_BP_SET_LOCKS ERTS_PROC_LOCK_MAIN @@ -1887,11 +1883,6 @@ erts_psd_set(Process *p, ErtsProcLocks plocks, int ix, void *data) #define ERTS_PROC_SCHED_ID(P, L, ID) \ ((UWord) erts_psd_set((P), (L), ERTS_PSD_SCHED_ID, (void *) (ID))) -#define ERTS_PROC_GET_DIST_ENTRY(P) \ - ((DistEntry *) erts_psd_get((P), ERTS_PSD_DIST_ENTRY)) -#define ERTS_PROC_SET_DIST_ENTRY(P, L, D) \ - ((DistEntry *) erts_psd_set((P), (L), ERTS_PSD_DIST_ENTRY, (void *) (D))) - #define ERTS_PROC_GET_SAVED_CALLS_BUF(P) \ ((struct saved_calls *) erts_psd_get((P), ERTS_PSD_SAVED_CALLS_BUF)) #define ERTS_PROC_SET_SAVED_CALLS_BUF(P, L, SCB) \ diff --git a/erts/emulator/test/distribution_SUITE_data/run.erl b/erts/emulator/test/distribution_SUITE_data/run.erl index f5169e160c..d5ed139369 100644 --- a/erts/emulator/test/distribution_SUITE_data/run.erl +++ b/erts/emulator/test/distribution_SUITE_data/run.erl @@ -30,16 +30,19 @@ from(H, [_ | T]) -> from(H, T); from(H, []) -> []. start() -> - net_kernel:start([fideridum,shortnames]), - {ok, Node} = slave:start(host(), heppel), - P = spawn(Node, a, b, []), - B1 = term_to_binary(P), - N1 = node(P), - ok = net_kernel:stop(), - N2 = node(P), - io:format("~w~n", [N1 == N2]), + Result = do_it(), + + %% Do GCs and node_and_dist_references + %% in an attempt to crash the VM (without OTP-13076 fix) + lists:foreach(fun(P) -> erlang:garbage_collect(P) end, + processes()), + erts_debug:set_internal_state(available_internal_state, true), + erts_debug:get_internal_state(node_and_dist_references), + + io:format("~w~n", [Result]), + if - N1 == N2 -> + Result -> init:stop(); true -> %% Make sure that the io:format/2 output is really written @@ -47,3 +50,29 @@ start() -> erlang:yield(), init:stop() end. + + +do_it() -> + {ok, _} = net_kernel:start([fideridum,shortnames]), + {ok, Node} = slave:start(host(), heppel), + P = spawn(Node, net_kernel, stop, []), + B1 = term_to_binary(P), + N1 = node(P), + ok = net_kernel:stop(), + N2 = node(P), + + %% OTP-13076 + %% Restart distribution with same node name as previous remote node + %% Repeat to wrap around creation + Result = lists:foldl(fun(_, Acc) -> + timer:sleep(2), % give net_kernel:stop() time to take effect :-( + {ok, _} = net_kernel:start([heppel,shortnames]), + N3 = node(P), + ok = net_kernel:stop(), + N4 = node(P), + Acc and (N3 =:= N1) and (N4 =:= N1) + end, + (N2 =:= N1), + lists:seq(1,3)), + + Result. |